Lancelot william wild and eric philip barfield



L. W. WILD AND E. P. BARFIELD.

METHOD OF AND MEANS FOR INDICATING THE CONDITION 0F STEEL, IRON, AND OTHER MAGNETIZABLE METALy DURING HEAT TREATMENT.

APPLICATION. FILED MAY 22. I9I8.

Patented Nov. 1I, 1919.

Figi.

UNITED sTATEs 'PATENT OFFICE.

LANCELOT WILLIAM WILD AND ERIC PHILIP BARFILD, 0F WESTMINSTER, LONDON, ENGLAND.

METHOD 0F AND MEANS FOR INDICATING TI-IE CONDITION OF. STEEL, IRON, 0B OTHER MAGNETIZABLE METAL DURING HEAT TREATMENT.

Specification of Letters Patent. Patented NOV. 11, 1919.

Application filed May 22, 1918. SerialNo. 285,935'.

To all whom t may concern:

Be it known that we, LANonLo'r WILLIAM WILD and ERIC PHILIP BARFIELD, both subjects of the King of Great Britain, and both residing at l/Vestminster Electrical Testing Laboratory, York Mansions, York street, Westminster, London, England, have invented a new and useful Improved Method of and Means for Indicating the Condition of Steel, Iron, or other Magnetizable Metal During Heat Treatment, of which the following is a specification.

Our inventionrelates to the method of determining the temperature to which steel or other magnetizable metal should be heated in hardening, tempering and annealing operations by means of an indication which is provided by the change in magnetic properties of the steel which takes place at that temperature. According to our invention, the steel or other metal under treatment is placed adj acent to a coil in a magnetic field, generated by means of a current which effects the heating of the metal, the indication that the critical temperature has been attained by the said metal being given by a current which is induced in the coil by the change in the magnetic flux due to the demagnetization of the steel at that critical temperature.

In practice we have found that diiiculty is sometimes met with if the source of current in the first coil is subject to fluctuation, since any small variation in the current in the said primary coil induces a current in the secondary coil which deiiects the galvanometer needle independently of the deilection which is caused on the change of condition of the steel or other metal in the furnace; as a result it is sometimes diii'cult to distinguish when the magnetic change of the metal actually takes place. To obviate this diiiculty we introduce into, or between, the primary and secondary circuits a compensating device,/the elements of which have the same inductance with respect to each other as have the primary and secondary coils of the furnace and are so arranged that the electromotiv'e forces generated in the two secondary circuits are in direct opposition to one another. The indicating device thus remains steady during small changes of current and is only appreciably affected by a change in the mutual induction of the furnace coils which is brought about when a magnetizable article is either introduced into or removed from the furnace, or loses its magnetic properties on attaining the temperature of decalescence.

This construction of apparatus .is also suitable for working with alternating current in which case when a piece of magnetizable metal is introduced into the furnace the mutual inductance between the furnace coils is increased whereby the balance between the electromotive forces in the two secondary coils is disturbed, the result being that an alternating current is caused to pass through the indicating instrument. When the metal becomes non-magnetic at the critical temperature the balance is restored so that the current ceases to iiow through the instru-' ment. Either of the'two mutual inductanccs` may be made adjustable and this will generally be found advisable in practice. For this purpose any convenient arrangement may be made use of such as an iron core, preferably slotted or laminated and adapted to be adjusted in position relatively to the windings of the compensating device. y

To enable the invention to be fully understood we will describe it by reference to the accompanying drawing, in which :4-

Figure 1 is an elevation of a suitable form of electric furnace for carrying out our improved process;

Fig. 2 is a sectional elevation at right angles to Fig. 1. l

Fig. 3 is a diagrammatic view of the modified construction of apparatus wherein a compensating device is combined with the furnace and indicatingdevice. and

Fig. 4 is a view similar to Fig. 3 illustrating the adaptation of the apparat-us to an alternating current.

Similar letters of reference refer to the same or corresponding parts throughout the several figures of the drawing.

Referring first to the arrangement shown in Figs. 1 and 2 a indicates a silica Crucible, tube or Inutile which is designed'to he partially filled with molten salt, such as potassium and sodium chlorids. and into which the object or material to be subjected to the heat treatment is introduced. The crucible or tube a has wound around its outer surface a heating coil b the ends of which are connected to the metal clips or bands c surrounding the said tube a, the said bands being in electrical connection by the wires @Z with metal bands c surrounding the top and bottom of an outer casing f, which incloses the silica tube or crucible a leaving an intervening space g`which is filled with a convenient heat and electrical insulating substance L, such as quartz powder.

c' is the second coil which is wound around the outside of the outer casing f, the ends of the said coil being connected to the metal bands j clamped upon the said casing f and the terminals of which are connected up in the circuit lf: which includes the galvanometer Z.

As will be understood, the apparatus is employed as follows,- that is to say, the furnace temperature is brought up to any suitable point by causing current to pass through the heating coil 6, the temperature attained being controlled by means of regulating resistances in the known manner. The article to be treated is then suspended within the molten salt in the crucible a and it immediately becomes magnetized by the current in the heating coil b. The said article is then gradually raised in temperature and on reaching that of decalescence it becomes non-magnetic. This change of condition induces in the second or outer coil i an electromotive force which exists until every part of the metal in the article under treatment has completed its change of condition. The electromotive force, which is thus set up in the outer coil by the said change of condition, causes a small current to flow through the latter, and this current is indicated by the deflection of the needle of the galvanometer Z from and back to the Zero point. When this visible indication is given by the galvanometer the operator knows with certainty that the article with- 1n the furnace is exactly at the temperature of decalescence.

Fig. 3 shows the combination with apparatus of the kind illustrated in Figs. l and 2, and above described, of a compensating device. It comprises the bobbin m which has wound around it the primary coil Z1 in series with the primary coil b of the furnace and the secondary coil l in series with the secondary coil z' of the furnace. As above described the two coils 1 and l are ofthe same relative inductance as that which exists between the primary and secondary colis Z) and Z and the polarity of the cminectlons, is, as shown, of such a nature that a small change in the magnitude of the current 1n the primary curcuit causes the elvetromotive forces which are thereby generated in the two secondary coils. and 'Z1 to be in direct opposition so that practically no current flows around the circuit and the galvancmeter Z remains steady. When, however, a magnetizable metal article kis either introduced into, or removed from, the crucible a, or loses its magnetic properties on attaining the temperature of decalescence, a change in the mutual inductance of the furnace coils Z and z' takes place so that a current is caused to flow through the secondary circuit and deliccts the needle of the galvanometer Z.

Fig. 4 shows the adaptation of the apparatus to working with an alternating current. It comprises the same elements as are shown in Fig. 3 but the compensating mutual inductance is furnished in addition with a core a the position of which relatively to the windings can be regulated so as to adjust the said inductance.

As above described when a magnetizable substance is introduced into the furnace the balance between the inductances is disturbed and an alternating current is caused to flow through the galvanometer Z, but when the substance becomes non-magnetic at the temperature of decalescense the balance is restored and the flow of current ceases, thus giving the indication required.

Having now particularly described and ascertained the nature oi' our said invention and in what manner the same is to be performed, we declare that what we claim is 1. The method of indicating the condition of steel, iron or other magnetizable metal during heat treatment, consisting in heating the metal by electric current which also generates a magnetic. field around the metal and in providing adjacent to the metal and in the said magnetic field a secondary coil in circuit with an indicating device through which current is induced by the change of magnetic conditions of the metal under treatment.

2. Apparatus for carrying out the process described in the preceding claimin clause, comprising a crucible tube or mu e heated by an electric coil or winding which also constitutes the magnetizing winding forthe material to be treated, and an outer casing carrying a secondary coil or windin in a circuit containing a galvanometer or like indicating device, substantially as heretofore described.

3. Apparatus for carrying out the process claimed in claim l, comprising a furnace including a crucible heated by an electric coil which also constitutes the magnetizing winding for the material to be treated, an outer casing carrying a secondary coil or winding in a circuit containing an indicating device and a compensating device in or between the primary and secondary electric circuits, the elements of the said compensating device having the same relative inductance as the primary and secondary coils of the furnace, substantially as, and for the purpose, hereinbefore described.

4. Apparatus for indicating the condition of steel, iron or other magnetizable metal during vheat treatment by the method dened by claim 1, comprising a furnace havingprimary and secondary coilseaoh in series with the corresponding coil of a compensating device, the pairscof coils having the same relative induotance and being so arranged that the electromotive forces genv as hereinbefore described.

5. In apparatus as defined in claim 4, the

combination with either of thetwo mutual A inductances of means, such as an' iron core` adjustable in position relatively to the inductance whereby the latter may be varied in value, substantially as hereinbefore described.

' LANCELOTWILLIAM WILD. ERIC PHILIP BARFIELD. 

